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Specific heat jump at superconducting transition in the presence of Spin-Density-Wave in iron-pnictides

We analyze the magnitude of the specific heat jump ΔC at the superconducting transition temperature T_c in the situation when superconductivity develops in the pre-existing antiferromagnetic phase. We show that ΔC/T_c differs from the BCS value and is peaked at the tri-critical point where this coexistence phase first emerges. Deeper in the magnetic phase, the onset of coexistence, T_c, drops and ΔC/T_c decreases, roughly as ΔC/T_c \propto T^2_c at intermediate T_c and exponentially at the lowest T_c, in agreement with the observed behavior of ΔC/T_c in iron-based superconductors.